Computations are exerted using the finite element method for (1) SPL of the cones which vibrate as a piston with and without a dust-cap, and (2) the changes of SPL at the normal modes of vibration of the dust-cap, with and without the air loading, and are compared with the measured results. In computation, the air loading of the back space of the cone is neglected, and the air chamber inside the dust-cap is assumed to be closed. Results are as follows : (1) The large dip of the sound pressure response caused by the concave shape radiation of the cone is diminished due to the dust-cap. The agreement between the computation and the measurement is good. (2) A dust-cap attached to the part of the largest displacement of the normal mode of the cone affects that normal mode severely. Computed sound pressure peak level of that normal mode, not considering the air loading, is extremely smaller than the measured result. Computed result, the air loading considered, agrees well with the measured result. (3) The lowest normal mode of the dust-cap, in which the dust-cap vibrates almost in the same phase, causes a fairly large sound pressure peak level.
